Fire resistance acoustic foam

ABSTRACT

A macmocellular foam is described having improved cell size and Fire-test-response Characteristics, among other features, which is obtained by selecting a particle size less than 1 micron for the flame retardant adjuvant. The inventors found that the amount of fire retardant adjuvant can be increased for a given foam cell size or the foam cell size can be increased for a given amount of fire retardant adjuvant, allowing the production of foams having exceptionally large, well-formed, cells that have excellent Fire-test-response Characteristics. The benefits are especially noteworthy in relation to thermoplastic foams and inorganic flame retardation adjuvants, due to the unexpected reduction in the nucleation effect of the adjuvant. The foams are useful for improving the acoustic performance of products that are required to meet certain Fire-test-response Characteristics. It may be used in automotive and other transportation devices, building and construction, household and garden appliances, power tool and appliance and electrical supply housing, connectors, and aircraft as acoustic systems for sound absorption and insulation.

[0001] Foams and foamed articles often find utility in acoustic systemsfor sound absorption and insulation. Such foams, when developed fordifferent market segments (appliance, automotive, building andconstruction, etc.) often need to meet certain acoustic performancerequirements and applicable Fire-test-response Characteristics (ASTM E176-99). To achieve the desired fire rating, a variety of flameretardant components are often added to such foam resin formulations.Unfortunately, the typical flame retardant components and otheradditives added to the polymer resin formulation cause a number ofproblems during the manufacture of the foam that have an adverse affecton obtaining acoustically active macrocellular foams. Flame retardantsoften cause poor cell structure and cell collapse due to their effectson the polymer gel viscosity and melt strength. To reduce the need forhigh concentrations of flame retardants, flame retardant adjuvants areoften added. Flame retardant adjuvants, however, also often are solidparticulate materials that act as nucleating agents in the foamingprocess and provide additional nucleation sites, resulting in theformation of a large number of small cells with variable properties.Unfortunately, small cell foam (average cell size less than 1 millimeter(mm) as determined by ASTM D3575) is not as desirable as large cellfoams (larger than 1 mm average cell size as determined by ASTM D3575)in certain end use applications, such as acoustic absorption.

[0002] U.S. Pat. No. 4,277,569 teaches the preparation of flameretardant polyolefin foams for thermal insulation and padding. However,the patent does not describe macrocellular foams or flame retardantmacrocellular foams for acoustic applications or their preparation.

[0003] Japanese Laid Open Patent Application No. 10-204200 describesolefin resin foams for use in vacuum molding made from 100 parts byweight of an olefin type resin comprising 30 to 90 percent by weightpropylene type resin and 70 to 10 percent by weight ethylene type resin,1 to 100 parts by weight of a brominated compound and 0.1 to 10parts byweight of antimony trioxide having an average particle size of 0.4microns or smaller. Macrocellular foams useful for acoustic applicationsare not described.

[0004] WO 00/15697 describes a macrocellular acoustically active foamwhich may be surface treated with a solution containing certain fireretardant materials. While that procedure is able to confer fireretardancy, it requires the extra steps of treating the foam afterextrusion and perforation and then drying the foam to remove the liquidmedia used to apply the fire retardant.

[0005] Therefore, a significant market need still exists for a largecell, acoustically active foam with good flame retardancy in which thefire retardant components are already in the polymer matrix of polymerfoams obtainable by conventional means. This need is not only generallyapplicable to polymer foams, but is also particularly acute in the areaof thermoplastic foams (that is, foams that are substantiallyuncrosslinked and capable of being remelted) and foams that alsoresistant water absorption such that they may be used in humid or wetenvironments without losing performance or potentiating corrosion ormicrobial growth problems. These and other problems as described below,are solved by the present invention.

[0006] One aspect of the present invention is macrocellular polymerfoams having an average cell size according to ASTM D3575 of at least1.5 mm, the foam containing at least one solid particulate flameretardant adjuvant, wherein the solid particulate flame retardantadjuvant has an average particle size less than one micron. The foamsalso preferably contain a flame retardant.

[0007] Another aspect of this invention is a process for makingmacrocellular polymer foams comprising extruding at an elevatedtemperature a foamable gel from a first region having a first pressureinto a second region having a second pressure less than the firstpressure to allow expansion of the foamable gel, the foamable gelcomprising at least one thermoplastic polymeric resin, at least oneblowing agent, and at least one solid particulate flame retardantadjuvant, wherein the solid particulate flame retardant adjuvant has aparticle size less than 1 micron. Included with this aspect are thefoamable gel intermediates and the polymer foams obtainable using thisprocess. The foamable gel also preferably contains a flame retardant.

[0008] Yet another aspect of this invention is a method for increasingthe maximum amount of solid particulate flame retardant adjuvant inmacrocellular foams having a given average cell size according to ASTMD3575 of at least 1.5 mm comprising decreasing the average particle sizeof the flame retardant adjuvant to a smaller average particle size thatis less than 1 micron.

[0009] Yet another aspect of this invention is a method for improvingthe acoustic absorption coefficient of macrocellular foams having agiven amount of solid particulate flame retardant adjuvant comprisingdecreasing the average particle size of the flame retardant synergist toa smaller average particle size that is less than 1 micron.

[0010] Another aspect of this invention is the use of the abovemacrocellular acoustic foam as an acoustic absorption or acousticinsulation material, particularly in environments in which fireretardancy is required, such as office partitions, automotivedecouplers, domestic appliances and machine enclosures.

Definitions

[0011] All references herein to elements or metals belonging to acertain Group refer to the Periodic Table of the Elements published andcopyrighted by CRC Press, Inc., 1989. Also any reference to the Group orGroups shall be to the Group or Groups as reflected in this PeriodicTable of the Elements using the IUPAC system for numbering groups.

[0012] Any numerical values recited herein include all values from thelower value to the upper value in increments of one unit provided thatthere is a separation of at least 2 units between any lower value andany higher value. As an example, if it is stated that the amount of acomponent or a value of a process variable such as, for example,temperature, pressure, time and the like is, for example, from 1 to 90,preferably from 20 to 80, more preferably from 30 to 70, it is intendedthat values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. areexpressly enumerated in this specification. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner. In particular,the end points of ranges for a particular subject are intended to befreely combinable with other stated ranges for the same subject unlessstated otherwise, for example, a stated lower end of a range may becombined with a stated upper end of a range for the same subject, suchas average cell size.

[0013] The term “micron” means one-millionth of a meter and isinterchangeable with the term “micrometer” and the abbreviation “μ”.

[0014] Unless stated otherwise, the term “flame retardant” when used byitself means a flame retardant which can be any compound or mixture ofcompounds which imparts flame resistance to the foam compositions of thepresent invention other than the solid particulate flame retardantsdescribed below as a solid particulate flame retardant adjuvant. Thisterm includes, but is not limited to, organic flame retardants such ashalogen-containing compounds or mixtures of compounds.

[0015] The term “solid particulate flame retardant adjuvant” means solidparticulate compounds which increase the flame resistance of the foamcompositions of the present invention when they are present in an amountof at least 1 part per hundred parts of total polymer resin (phr).Preferably they enhance the effectiveness of flame-retardants that arepresent in the polymer matrix of the foam in a form other than as solidparticles, such as most organic flame retardants. This term is intendedto include, but not be limited to, solid particulate flame retardantsynergists, char forming materials, smoke suppressants and solidparticulate flame retardants. They are preferably primarily comprised ofan inorganic compound or a mixture of inorganic compounds. Unlessotherwise specified herein, the term “flame retardant adjuvant” whenused in the context of the present invention means “solid particulateflame retardant adjuvant” and the terms “flame retardant synergist” and“synergist” when used in the context of the present invention means“solid particulate flame retardant synergist”. The flame retardantsynergists are encompassed by the more generic term “solid particulateflame retardant adjuvant”. The latter applies by analogy to the solidparticulate char forming materials and smoke suppressants, but thedistinction in wording is maintained herein between the expression“flame retardant” (without the term “adjuvant”) and the expression“solid particulate flame retardant”.

[0016] The term “flame retardant package” means a combination of flameretardant(s) and flame retardant adjuvant(s) with each other. A typicalexample is a combination of flame retardant(s), flame retardantsynergist(s), and optionally smoke suppressant(s).

[0017] The term “interpolymer” is used herein to indicate a polymerwherein at least two different monomers are polymerized to make theinterpolymer. This includes copolymers, terpolymers, etc.

[0018] The term “macrocellular acoustic foam” is used herein to indicatea foam having an average cell size according to ASTM D3575 greater of atleast 1.5 mm, more preferably at least 2 mm, even more preferably atleast 3 mm, even more preferably at least 4 mm, preferably up to 20 mm,also preferably up to 15 mm, and for some end uses up to 10 mm isparticularly preferred. At a thickness of 35 mm, macrocellular foams mayhave an average sound absorption coefficient (measured via ASTM E1050 at250, 500, 1000 and 2000 hertz (Hz) sound frequencies) of greater than0.15, preferably greater than 0.20, more preferably greater than 0.25,even more preferably greater than 0.30.

Flame Retardant Adjuvant

[0019] Examples of solid particulate flame retardant adjuvants are solidparticulate flame retardant synergists, char forming materials, smokesuppressants, and solid particulate flame retardants.

[0020] Flame retardant synergists include, but are not limited to, metaloxides (e.g., iron oxide, tin oxide, zinc oxide, aluminum trioxide,alumina, antimony trioxide and antimony pentoxide, bismuth oxide,molybdenum trioxide, and tungsten trioxide), zinc borate, antimonysilicates, zinc stannate, zinc hydroxystannate, ferrocene and mixturesthereof, antimony trioxide and antimony pentoxide being preferred.Antimony trioxide having an average particle size less than 1 micron isavailable as a concentrate in low density polyethylene (LDPE) from GreatLakes Chemical Corporation under the trademark MICROFINE™ and antimonypentoxide having an average particle size less than 0.1 micron isavailable under the trademark. NYACOL™ from Nyacol Nano Technologies,Inc. Ashland, Mass., U.S.A.

[0021] Solid particulate char forming materials include, but are notlimited to, clay fillers, such as organoclay nanocomposites. Organoclaynanocomposites having an effective particle size less than 1 micronafter incorporation into the polymer matrix of a polymer foam of thepresent invention are available under the trademark CLOISITE™ fromSouthern Clay Products, Inc., Gonzales, Tex., U.S.A.

[0022] Solid particulate smoke suppressants include, but are not limitedto, zinc borate, tin oxide, and ferric oxide. Zinc borate, molybdenumtrioxide and alumina having an average particle size less than 0.5microns are available from Nyacol Nano Technologies, Inc.

[0023] Solid particulate flame retardants include inorganic fireretardants, such as magnesium hydroxide, having a particle size in therange from less than 1 micron to at least 2 nanometers. An example ismagnesium hydroxide available from Nyacol Nano Technologies, Inc., whichis reported to have an average particle size of 0.225 microns.

[0024] The flame retardant adjuvants may be used individually or incombination with each other. They, and other flame retardant adjuvantshaving the required and preferred particle sizes, may be made usingtechniques well known in the art, and may be incorporated into thepolymer matrix. See, for example, U.S. Pat. No. 5,409,980, whichdescribes synergists and combinations of the same with flame retardantssuitable for the present invention.

[0025] An important aspect of this invention is the selection of theaverage particle size of the flame retardant adjuvant. The conventionalview was that increasing the amount of small particle inorganic flameretardant adjuvant would inevitably decrease polymer foam cell size dueto nucleation caused by large numbers of adjuvant particles in thepolymer melt prior to the foaming step. The inventors have found thatdecreasing the average particle size to a range of from less than about1 micron to about 2 nanometers, either as supplied or afterincorporation into the polymer matrix of a polymer foam according tothis invention, unexpectedly increases the amount by weight of theadjuvant that can be added to the foam while simultaneously maintainingor increasing the average cell size of the macrocellular polymer foammeasured according to ASTM D3575. In a preferred embodiment, 99 percentof the particles have a particle size less than 1 micron, morepreferably 99.9 percent of the particles have a particle size less than1 micron.

[0026] The average particle size of the flame retardant adjuvant ispreferably not greater than 0.5 micron, and more preferably not greaterthan 0.3 micron.

[0027] In a particularly preferred embodiment, the average particle sizeis not greater than 0.1 micron, more preferably not greater than 0.01micron, down to about 0.002 micron (2 nanometers), which is in thecolloidal particle size range. In this embodiment, at least 99 percentof the particles preferably have a particle size less than 0.1 micron.

[0028] The average particle size referred to above is the volumetricaverage particle size. The particle size of the flame retardant adjuvantas such may be measured by appropriate conventional particle sizemeasuring techniques such as sedimentation, photon correlationspectroscopy, field flow fractionation, disk centrifugation,transmission electron spectroscopy, and dynamic light scattering. Apreferred technique is to measure dynamic light scattering using adevice such as a Horiba LA-900 Laser Scattering particle size analyzer(Horiba Instruments, Irvine, Calif., USA). The volumetric distributionrelates to the weight distribution.

[0029] When the flame retardant adjuvant is in the foam polymer matrix,the average particle size may be determined using techniques known inthe art. One approach is to use an electron microprobe, such as a CamecaSX-50 electron microprobe, to collect element maps of the particles froma cross-section of the foam and then use a scanning electron microscope,such as a JEOL 6320 field emission scanning electron microscope, tocreate an image of the mapped particles to examine their surface andcross-sectional features. By overlaying the elemental map over theinformation derived from the scanning electron microscope image, one canselectively determine the average particle size of the flame retardantadjuvant in question.

[0030] The beneficial effect of this invention is preferably obtainedwith each solid particulate flame retardant adjuvant present in thefoam. When multiple flame retardant adjuvants of substantially differentchemical composition are present, the term “average particle size”refers to the average particle size of the flame retardant adjuvanthaving the largest particle size unless stated expressly to the contraryherein. When multiple flame retardant adjuvants are present in a foamthat are detectable, but chemically indistinguishable from one anotherusing an electron microprobe, their particle size measurements may becombined to obtain the average particle size of the flame retardantsynergist.

[0031] The required and preferred particle sizes may be obtained usingvarious milling processes and equipment, such as the process andequipment described in U.S. Pat. No. 5,695,691, which is herebyincorporated herein by reference, by chemical peptization, formation ofcolloidal sized particles in a plasma with subsequent dispersion of theparticles in a suitable continuous phase, by the ion exchange methoddescribed in U.S. Pat. No. 3,860,523, U.S. Reissue 31,214 and U.S. Pat.No. 4,110,247.

[0032] The particles may be treated to reduce agglomeration or improvedispersibility in certain media and, as in the case of colloidalantimony pentoxide, the particles may be treated to reduce degradationof the polymer resin while the resin is at an elevated temperature, suchas during extrusion of the foam of this invention, as taught in, forinstance, U.S. Pat. No. 4,741,865. WO 00/64966 describes how to makecertain vacuum de-aerated powdered polymer additives having a particlesize range overlapping the less than one micron range, including flameretardant adjuvants suitable for use in the foams of this invention.Each of the above patents and published patent applications areincorporated herein by reference for their relevant disclosure.

[0033] The amount of inorganic flame retardant adjuvant is preferably atleast 1 phr, more preferably at least 2 phr, preferably up to about 6phr.

[0034] Optionally, adjuvants other than the solid particulate flameretardant adjuvants used in this invention may be added to the polymericresin composition. Examples of such adjuvants include certain organicflame retardant synergists that are known to cause cell nucleation infoams, such as dicumyl(dimethyldiphenylbutane),poly(1,4-diisopropylbenzene), halogenated paraffin, triphenylphosphate,and mixtures thereof.

Flame Retardant

[0035] The foams of the invention preferably include a flame retardantwhich functions to slow or minimize the spread of fire in the foam. Theflame retardant is preferably a halogen-containing compound or mixtureof compounds which imparts flame resistance to the foams of the presentinvention.

[0036] The term “halo” or “halogenated” includes compounds containingbromine, chlorine, or fluorine, or any combination thereof. Preferably,the flame retardant is a bromine or chlorine-containing compound. Theymay be halogenated aromatic or alkane compounds.

[0037] Suitable aromatic halogenated flame retardants are well-known inthe art and include but are not limited to hexahalodiphenyl ethers,octahalodiphenyl ethers, decahalodiphenyl ethers, decahalodiphenylethanes; 1,2-bis(trihalophenoxy)ethanes;1,2-bis(pentahalophenoxy)ethanes; a tetrahalobisphenol-A; ethylene(N,N′)-bis-tetrahalophthalimides; tetrabromobisphenol A bis(2,3-dibromopropyl ether); tetrahalophthalic anhydrides;hexahalobenzenes; halogenated indanes; halogenated phosphate esters;halogenated polystyrenes; and polymers of halogenated bisphenol-A andepichlorohydrin, and mixtures thereof. Preferred aromatic halogenatedflame retardants may include one or more of tetrabromobisphenol-A(TBBA), tetrabromo bisphenol A bis (2,3-dibromopropyl ether),decabromodiphenyl ethane, brominated trimethylphenylindane, or aromatichalogenated flame retardants with similar kinetics.

[0038] Suitable halogenated alkane compounds may be branched orunbranched, cyclic or acyclic. Preferably, the halogenated alkanecompound is cyclic. Suitable halogenated alkane flame retardants includeand are not limited to hexahalocyclododecane; tetrabromocyclooctane;pentabromochlorocyclohexane; 1,2dibromo-4-(1,2-dibromoethyl)cyclohexane;1,1,1,3-tetrabromononane; and mixtures thereof. Preferred halogenatedalkane flame retardant compounds include hexabromocyclododecane and itsisomers, pentabromochlorocyclohexane and its isomers, and1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane and its isomers.Hexabromocyclododecane (HBCD), and halogenated alkane flame retardantswith similar kinetics are preferred.

[0039] Commercially available products suitable for use as flameretardants in the present invention include PE-68™ (a trademark andproduct of the Great Lakes Chemical Corporation). Suitable flameretardants are well known, and include brominated organic compounds suchas are described in U.S. Pat. No. 4,446,254 and U.S. Pat. No. 5,171,757,the entire contents of which are herein incorporated by reference. Forfoams, the halogen content provided by the halogenated flame retardantsin the final foams should be 0.05-20 phr, preferably 0.1-15 phr and mostpreferably 0.5-15 phr.

[0040] The polymeric resin compositions preferably include at leastabout 0.5 phr halogenated flame retardant, more preferably at leastabout 0.8 phr, preferably up to about 12 phr, more preferably up toabout 6 phr halogenated flame retardant. The parts per hundred parts ofresin (“phr”) are based on the total parts by weight of polymer in theflame retardant-containing composition.

[0041] In a preferred embodiment, the flame retardant is ahexahalocyclododecane, preferably hexabromocyclododecane (HBCD), ortetrabromobisphenol A bis (2,3-dibromopropyl ether), PE™-68, or acombination with any other halogenated or non-halogenatedflame-retardants, which can include, but are not limited to phosphorousbased flame retardants such as triphenyl phosphate and encapsulated redphosphorous.

[0042] In a preferred embodiment, the flame retardant is a mixture of atleast two different types of flame retardants that may be added togetheror separately into a polymer resin composition. A mixture that includesboth a halogenated alkane compound and an aromatic halogenated compoundhas been found to enhance blending of α-olefin polymers with alkenylaromatic polymers which are described in more detail under separateheadings below, and this combination tends to reduce the density offoams made from that mixture. The ratio of aromatic halogenated flameretardant to halogenated alkane flame retardant in parts by weight forthat purpose is preferably from about 16:1 to 1:16, more preferably fromabout 7.5:1 to 1:7.5, and most preferably about 5:1 to 1:5. Theconcentration of aromatic halogenated flame retardant is preferably atleast about 0.5 parts by weight per hundred parts by weight (phr) of theα-olefin polymer component, more preferably at least 1 phr, andpreferably up to 8 phr based on the weight of the α-olefin polymercomponent. The concentration of halogenated alkane flame retardant ispreferably at least about 0.5 parts by weight per hundred parts byweight (phr) of the alkenyl aromatic polymer component, more preferablyat least 1 phr, and preferably up to 8 phr based on the weight of thealkenyl aromatic polymer component. In a preferred embodiment, the flameretardant mixture includes a combination of hexahalocyclododecane suchas hexabromocyclododecane (HBCD), and tetrabromobisphenol A bis(2,3-dibromopropyl ether).

[0043] Synergistic combinations, such as mixtures of one or morehalogenated compounds and one or more flame retardant synergists,typically are used preferably at a ratio of 0.25 to 25, preferably 0.5to 15, more preferably from 0.5 to 12 parts by weight flame retardanthalogen to 1 part by weight of flame retardant synergist. In the case ofan antimony-containing synergist, the ratio of halogen contained in thehalogenated flame retardant to antimony contained in the flame retardantsynergist is preferably in the range from 1 to 7 moles, more preferably1 to 6 moles, and even more preferably 1 to 4 moles, halogen contributedby the flame retardant per mole antimony contributed by the flameretardant synergist.

Stability Control Agent or Cell Size Enlarging Agent

[0044] A stability control agent or cell size enlarging agent isoptionally added to the present foam to enhance dimensional stability.Preferred agents include amides and esters of C10-24 fatty acids. Suchagents are seen in U.S. Pat. Nos. 3,644,230 and 4,214,054, which areincorporated herein by reference. Most preferred agents include stearylstearamide, glycerol monostearate (available from ICI Americas Inc.,under the trademark Atmer™ 129), glycerol monobehenate, and sorbitolmonostearate. Typically, such stability control agents are employed inan amount ranging from 0.1 to 10 phr.

Other Additives

[0045] The foam of the present invention may optionally contain one ormore conventional additives to the extent the additives do not interferewith the desired foam properties. Typical additives include antioxidants(such as hindered phenols (for example, Irganox™ 1010, trademark of andavailable from the Ciba Geigy Corporation), ultraviolet stabilizers,colorants, pigments, fillers, acid scavengers, and extrusion aids. Inaddition, a nucleating agent may optionally be added in order to controlthe size of foam cells, if necessary.

Polymer

[0046] The polymer used to make the foam may be any polymer capable offormiing a foam structure. Preferred polymers are thermoplasticpolymers, such as α-olefin polymers, vinyl aromatic polymers, andethylene-styrene interpolymers, and combinations (for example, blends)thereof, as further described below.

[0047] Preferably the resin to be foamed comprises an ethylene orα-olefin homopolymer resin or a blend of one or more of said ethylene orC₃-C₂₀ α-olefin homopolymers. The resin to be foamed can also comprise ablend of one or more of said ethylene or C₃-C₂₀ α-olefin homopolymerswith a second polymer component. This second polymer component caninclude, but is not limited to, ethylene/C₃-C₂₀ α olefin intetpolyiners(including polyolefin elastomers, and polyolefm plastomers) or one ormore substantially random interpolymers, or combinations thereof.

[0048] 1. α-Olefin Polymers The α-olefin polymers are polymers orinterpolymers containing repeated units derived by polymerizing anα-olefin. As defined herein, the α-olefin polymer contains essentiallyno polymerized monovinylidene aromatic monomers and no stericallyhindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.Particularly suitable α-olefins have from 2 to about 20 carbon atoms,preferably from 2 to about 8 carbon atoms, and include ethylene,propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and thelike. Preferred α-olefin polymers are homopolymers of ethylene orpropylene and interpolymers of ethylene with a C₃-C₈ α-olefin. Theα-olefin polymer may also contain, in polymerized form, one or moreother non-aromatic monomers that are interpolymerizable with theα-olefin and which contain an aliphatic or cycloaliphatic group. Suchmonomers include, for example, vinyl acetate, acrylic acid, methacrylicacid, esters of acrylic or methacrylic acid and acid anhydrides such asmaleic anhydride. The α-olefin polymer preferably contains at least 75percent by weight, preferably at least 95 percent by weight, ofpolymerized α-olefin monomers. More preferably, the α-olefin polymercontains at least 85 percent by weight polymerized ethylene, withpolymerized α-olefin monomers constituting the remainder of the polymer.In other words, the α-olefin polymer may contain polyethylene or acopolymer of ethylene and up to about 15 percent of another α-olefin.

[0049] Particularly suitable α-olefin polymers include low densitypolyethylene (LDPE), which term is used herein to designate polyethylenehomopolymers made in a high pressure, free radical polymerizationprocess. These LDPE polymers are characterized by having a high degreeof long chain branching. LDPE useful in this invention preferably has adensity of about 0.910 to 0.970 g/cc (ASTM D792) and a melt index fromabout 0.02 to about 100 grams per 10 minutes (g/10 min), preferably from0.2 to about 30 grams per 10 minutes (as determined by ASTM Test MethodD 1283, condition 190° C./2.16 kg). LDPE employed in the presentcomposition preferably has a density of less than or equal to 0.935 g/cc(ASTM D792) and a melt index from 0.05 to 50, more preferably from 0.1to 20, grams per 10 minutes (as determined by ASTM Test Method D1238,Condition 190°/2.16).

[0050] The so-called linear low density polyethylene (LLDPE) and highdensity polyethylene (HDPE) products are also useful herein. Thesepolymers are homopolymers of polyethylene or copolymers thereof with oneor more higher α-olefins and characterized by the near or total absence(less than 0.01/1000 carbon atoms) of long chain branching. LLDPE andHDPE are made in a low pressure process employing conventionalZiegler-Natta type catalysts, as described in U.S. Pat. No. 4,076,698.LLDPE and HDPE are generally distinguished by the level of α-olefincomonomer that is used in their production, with LLDPE containing higherlevels of comonomer and accordingly lower density. Suitable LLDPEpolymers having a density of from about 0.85 to about 0.940 g/cc (ASTMD792) and a melt index (ASTM D1238, condition 190° C./2.16 kg) of about0.01 to about 100 grams/10 minutes. Suitable HDPE polymers have asimilar melt index, but have a density of greater than about 0.940 g/cc.

[0051] LLDPE polymers having a homogeneous distribution of the comonomerare described, for example, in U.S. Pat. No. 3,645,992 to Elston andU.S. Pat. Nos. 5,026,798 and 5,055,438 to Canich.

[0052] Yet another type of α-olefin polymer are substantially linearolefin polymers as described in U.S. Pat. Nos. 5,272,236 and 5,278,272,incorporated herein by reference. The substantially linear olefinpolymer is advantageously a homopolymer of a C₂-C₂₀ α-olefin or,preferably, an interpolymer of ethylene with at least one C₃-C₂₀α-olefin and/or a C₄-C₁₈ diolefin. These polymers contain a small amountof long-chain branching (i.e. about 0.01 to 3, preferably 0.01-1 andmore preferably 0.3-1 long chain branch per 1000 carbon atoms) andtypically exhibit only a single melting peak by differential scanningcalorimetry. Particularly suitable substantially linear olefin polymershave a melt index (ASTM D1238, Condition 190° C./2.16 kg) of from about0.01 to about 1000 g/10 min, and a density of from 0.85 to 0.97 g/cc,preferably 0.85 to 0.95 g/cc and especially 0.85 to 0.92 g/cc. Examplesinclude polyolefin plastomers, such as those marketed by The DowChemical Company under the trademark AFFINITY™ and polyethyleneelastomers, such as those marketed by Du Pont Dow Elastomers LLC underthe trademark ENGAGE™.

[0053] Another suitable α-olefin polymer includes propylene polymers.The term “propylene polymer” as used herein means a polymer in which atleast 50 weight percent of its monomeric units are derived directly frompropylene. Suitable ethylenically unsaturated monomers other thanpropylene that may be included in the propylene polymer, includeα-olefins, vinylacetate, methylacrylate, ethylacrylate, methylmethacrylate, acrylic acid, itaconic acid, maleic acid, and maleicanhydride. Appropriate propylene interpolymers include random, block,and grafted copolymers or interpolymers of propylene and an olefinselected from the group consisting of ethylene, C₄-C₁₀ 1-olefins, andC₄-C₁₀ dienes. Propylene interpolymers also include random terpolymersof propylene and 1-olefins selected from the group consisting ofethylene and C₄-C₈ 1-olefins. The C₄-C₁₀ 1-olefins include the linearand branched C₄-C₁₀ 1-olefins such as, for example, 1-butene,isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene,3,4-dirnethyl-1-butene, 1-heptene, 3-methyl-1-hexene and the like.Examples of C₄-C₁₀ dienes include 1,3-butadiene, 1,4-pentadiene,isoprene, 1,5-hexadiene, and 2,3-dimethyl-1,3-hexadiene. As used herein,the term “interpolymers” means polymers derived from the reaction of twoof more different monomers and includes, for example, copolymers andterpolymers.

[0054] The propylene polymer material may be comprised solely of one ormore propylene homopolymers, one or more propylene copolymers, andblends of one or more of each of propylene homopolymers and copolymers.The polypropylene preferably comprises at least 70, even more preferablyat least 90, and even more preferably 100, weight percent propylenemonomer derived units (that is, the propylene homopolymers arepreferred).

[0055] The propylene polymer preferably has a weight average molecularweight (M_(W)) of at least 100,000. M_(W) can be measured by knownprocedures.

[0056] The propylene polymer also preferably has a branching index lessthan 1. The branching index is an approach to quantifying the degree oflong chain branching selected for this particular invention. Thedefinition of branching index and procedure for determining the same isdescribed in column 3, line 65 to column 4, line 30, of U.S. Pat. No.4,916,198, which is incorporated herein by reference. The branchingindex is more preferably less than 0.9, and even more preferably lessthan 0.4.

[0057] The propylene polymer has a tan δ value not greater than 1.5,preferably not greater than 1.2, even more preferably not greater than1.0, and even more preferably not greater than 0.8. Tan δ may becalculated from g″/g′, where g″ is the loss modulus of the propylenepolymer and g′ is storage modulus of the propylene polymer melt using a2.5 mm thick and 25 mm diameter specimen of the propylene polymer at 190C at a one Radian per second oscillating frequency. These parameters maybe measured using a mechanical spectrometer, such as a Rheometrics ModelRMS-800 available from Rheometrics, Inc., Piscataway, N. J., U.S.A.Further details of how to carry out this determination of the tan δ, g′and g″ values is provided in column 5, lines 59 to 64, and column 6,lines 4 to 29, of U.S. Pat. No. 5,527,573, which is incorporated hereinby reference.

[0058] In addition or in the alternative, the propylene polymerpreferably has a melt tension of at least 7 centiNewtons (cN), morepreferably at least 10 cN, and even more preferably at least 15 cN, andeven more preferably at least 20 cN. Preferably, the propylene polymerhas a melt tension not greater than 60 cN, more preferably not greaterthan 40 cN. The term “melt tension” as used throughout this descriptionrefers to a measurement of the tension in cN of a strand of moltenpolymer material at extruded from a capillary die with an diameter of2.1 mm and a length of 40 mm at 230° C. at an extrusion speed of 20mm/minute (min.) and a constant take-up speed of 3.14 meter/minute usingan apparatus known as a Melt Tension Tester Model 2 available from ToyoSeiki Seisaku-sho, Ltd. This method for determining melt tension issometimes referred to as the “Chisso method”.

[0059] In addition or in the alternative, the propylene polymerpreferably has a melt strength of at least 10 centiNewtons (cN), morepreferably at least 20 cN, and even more preferably at least 25 cN, andeven more preferably at least 30 cN. Preferably, the propylene polymerhas a melt strength not greater than 60 cN, more preferably not greaterthan 55 cN. The term “melt strength” throughout this description refersto a measurement of the tension in cN of a strand of molten polymermaterial extruded from a capillary die with an diameter of 2.1 mm and alength of 41.9 mm at 190° C. at a rate of 0.030 cc/sec. and stretched ata constant acceleration to determine the limiting draw force, orstrength at break, using an apparatus known as a Gottfert Rheotens™ melttension apparatus available from Gottfert, Inc.

[0060] The propylene polymer used in the process of the inventionpreferably also has a melt elongation of at least 100 percent, morepreferably at least 150 percent, most preferably at least 200 percent asmeasured by the same Rheotens™ melt tension apparatus and generalprocedure described above.

[0061] The propylene polymer material preferably also has a melt flowrate of at least 0.01 more preferably at least 0.05, even morepreferably at least 0.1 g/l 0 min., and even more preferably at least0.5 g/l0 min. up to 100, more preferably up to 50, even more preferablyup to 20, and even more preferably up to 10, g/10 min. Throughout thisdescription, the term “melt flow rate” refers to a measurement conductedaccording to American Society for Testing and Materials (ASTM) D1238condition 230° C./2.16 kg. (aka Condition L).

[0062] In addition, α-olefin polymers that have been subjected tocoupling or light crosslinking treatments are useful herein, providedthat they remain melt processable. Such grafting or light crosslinkingtechniques include silane grafting as described in U.S. Pat. No.4,714,716 to Park; peroxide coupling as described in U.S. Pat. No.4,578,431 to Shaw et al., and irradiation as described in U.S. Pat. No.5,736,618 to Poloso. Preferably, the treated polymer has a gel contentof less than 10 percent, more preferably less than 5 percent, mostpreferably less than 2 percent by weight, as determined by gelpermeation chromatography. Treatment of this type is of particularinterest for HDPE, LLDPE or substantially linear polyethylenecopolymers, as it tends to increase the melt tension and melt viscosityof those polymers to a range that improves their ability to be processedinto foam in an extrusion process.

[0063] Preferred propylene polymers include those that are branched orlightly cross-linked. Branching (or light cross-linking) may be obtainedby those methods generally known in the art, such as chemical orirradiation branching/light cross-linking. One such resin which isprepared as a branched/lightly cross-linked polypropylene resin prior tousing the polypropylene resin to prepare a finished polypropylene resinproduct and the method of preparing such a polypropylene resin isdescribed in U.S. Pat. No. 4,916,198, which is hereby incorporated byreference. Another method to prepare branched/lightly cross-linkedpolypropylene resin is to introduce chemical compounds into theextruder, along with a polypropylene resin and allow thebranching/lightly cross-linking reaction to take place in the extruder.This method is illustrated in U.S. Pat. Nos. 3,250,731 with apolyfunctional azide, U.S. Pat. No. 4,714,716 (and publishedInternational Application WO 99/10424) with an azidoftmctional silaneand EP 879,844-A1 with a peroxide in conjunction with a multi-vinylfunctional monomer. The aforementioned U.S. patents are incorporatedherein by reference. Irradiation techniques are illustrated by U.S Pat.Nos. 5,605,936 and 5,883,151, which are also incorporated by reference.The polymer composition used to prepare the foam preferably has a gelcontent of less than 10 percent, more preferably less than 5 percent,per ASTM D2765-84, Method A.

[0064] If an ethylene polymer, such as the ethylene homopolymer, isblended with a propylene polymer, the weight ratio of the propylenepolymer to the ethylene polymer is preferably at least 35:65, morepreferably at least 1: 1, preferably up to 9:1, and more preferably upto 7:1. Such blends may optionally contain at least one substantiallyrandom interpolymer, such as an ethylene/styrene interpolymer, asdescribed under a separate heading below. An advantage of these foams isthe ability to use it in locations where a high service temperature isrequired and yet have a foam that is thermoformable and potentiallyrecyclable. An example is in the compartment of a motor, such as aninternal combustion engine, such as found on a vehicle, electricgenerator, compressor or pump. An indication of high service temperatureis resistance to heat distortion at elevated temperatures. As usedherein, the expression, “heat distortion temperature” refers to themaximum temperature at which the foam body does not shrink more than 5percent by volume during an exposure to that temperature for one hour.Preferably the heat distortion temperature of the foams according to thepresent invention is at least 130° C., more preferably at least 140° C.,and even more preferably at least 150° C.

[0065] 2. Alkenvl Aromatic Polymer

[0066] For purposes of this invention, the alkenyl aromatic polymer ofthe polymer blend is a melt-processable polymer or melt processableimpact-modified polymer in the form of polymerized monovinylidenearomatic monomers as represented by the structure:

H₂C═CRAr

[0067] wherein R is hydrogen or an alkyl radical that preferably has nomore than three carbon atoms and Ar is an aromatic group. R ispreferably hydrogen or methyl, most preferably hydrogen. Aromatic groupsAr include phenyl and naphthyl groups. The aromatic group Ar may besubstituted. Halogen (such as C1, F, Br), alkyl (especially C₁-C₄ allylsuch as methyl, ethyl, propyl and t-butyl), C₁-C₄ haloalkyl (such aschloromethyl or chloroethyl) and alkoxyl (such as methoxyl or ethoxyl)substituents are all useful. Styrene, para-vinyl toluene, α-methylstyrene, 4-methoxy styrene, t-butyl styrene, chlorostyrene, vinylnaphthalene and the like are all useful monovinylidene aromaticmonomers. Styrene is especially preferred.

[0068] The alkenyl aromatic polymer may be a homopolymer of amonovinylidene aromatic monomer as described above. Polystyrenehomopolymers are the most preferred alkenyl aromatic polymers.Interpolymers of two or more monovinylidene aromatic monomers are alsouseful.

[0069] Although not critical, the alkenyl aromatic polymer may have ahigh degree of syndiotactic configuration; that is, the aromatic groupsare located alternately at opposite directions relative to the mainchain that consists of carbon-carbon bonds. Homopolymers ofmonovinylidene aromatic polymers that have syndiotacticity of 75 percentr diad or greater or even 90 percent r diad or greater as measured by¹³C NMR are useful herein.

[0070] The alkenyl aromatic polymer may also contain repeating unitsderived from one or more other monomers that are copolymerizable withthe monovinylidene aromatic monomer. Suitable such monomers includeN-phenyl maleimide; acrylamide; ethylenically unsaturated nitriles suchas acrylonitrile and methacrylonitrile; ethylenically unsaturatedcarboxylic acids and anhydrides such as acrylic acid, methacrylic acid,fumaric anhydride and maleic anhydride; esters of ethylenicallyunsaturated acids such as C₁-C₈ alkyl acrylates and methacrylates, forexample n-butyl acrylate and methyl methacrylate; and conjugated dienessuch as butadiene or isoprene. The interpolymers of these types may berandom, block or graft interpolymers. Blends of interpolymers of thistype with homopolymers of a monovinylidene aromatic monomer can be used.For example, styrene/C₄-C₈ alkyl acrylate interpolymers andstyrene-butadiene interpolymers are particularly suitable as impactmodifiers when blended into polystyrene. Such impact-modifiedpolystyrenes are useful herein.

[0071] In addition, the alkenyl aromatic polymers include those modifiedwith rubbers to improve their impact properties. The modification canbe, for example, through blending, grafting or polymerization of amonovinylidene aromatic monomer (optionally with other monomers) in thepresence of a rubber compound. Examples of such rubbers are homopolymersof C₄-C₆ conjugated dienes such as butadiene or isoprene;ethylene/propylene interpolymers; interpolymers of ethylene, propyleneand a nonconjugated diene such as 1,6-hexadiene or ethylidene norbomene;C₄-C₆ alkyl acrylate homopolymers or interpolymers, includinginterpolymers thereof with a C₁-C₄ alkyl acrylate. The rubbers areconveniently prepared by anionic solution polymerization techniques orby free radical initiated solution, mass or suspension polymerizationprocesses. Rubber polymers that are prepared by emulsion polymerizationmay be agglomerated to produce larger particles having a multimodalparticle size distribution.

[0072] Preferred impact modified alkenyl aromatic polymers are preparedby dissolving the rubber into the monovinylidene aromatic monomer andany comonomers and polymerizing the resulting solution, preferably whileagitating the solution so as to prepare a dispersed, grafted, impactmodified polymer having rubber domains containing occlusions of thematrix polymer dispersed throughout the resulting polymerized mass. Insuch products, polymerized monovinylidene aromatic monomer forms acontinuous polymeric matrix. Additional quantities of rubber polymer maybe blended into the impact modified polymer if desired.

[0073] Commercial PS (polystyrene), HIPS (high impact polystyrene), ABS(acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) resinsthat are melt processable are particularly useful in this invention.

[0074] The alkenyl aromatic polymer has a molecular weight such that itcan be melt processed with a blowing agent to form a cellular foamstructure. Preferably, the alkenyl aromatic polymer has a meltingtemperature of about 60° C. to about 310C and a melt flow rate of about0.5 to about 50 grams per 10 minutes (American Society for Testing andMaterials (ASTM) test D1238, 200° C./5 kg). A weight average molecularweight of about 60,000 to about 350,000, preferably from about 100,000to about 300,000, is particularly suitable. In the case of an impactmodified polymer, these molecular weight numbers refer to molecularweight of the matrix polymer (that is, the continuous phase polymer of amonovinylidene aromatic monomer).

[0075] The aromatic polymer may be blended with the α-olefin polymer,optionally in the presence of a compatibilizer. Such a polymer blendpreferably contains from about 10 percent, more preferably from about 30percent, more preferably from about 40 percent up to about 90 percent,more preferably up to about 70 percent, and more preferably up to about60 percent by weight of the α-olefin polymer based on the combinedweight of alkenyl aromatic polymer, α-olefin polymer, and polymericcompatibilizer. Suitable compatibilizers include certain aliphaticα-olefin/monovinylidene aromatic interpolymers such as the substantiallyrandom interpolymers described under a separate heading below,hydrogenated or non-hydrogenated monovinylidene aromatic/conjugateddiene block (including diblock and triblock) copolymers, andstyrene/olefin graft copolymers. The term “interpolymer” is used hereinto indicate a polymer wherein at least two different monomers arepolymerized to make the interpolymer. This includes copolymers,terpolymers, etc.

[0076] Although the flame retardant package is discussed separately, theflame retardant package may also act as a compatibilizer in that itminimizes macroscopic phase separation of the polymer blend. Ifsufficient quantities of the flame retardant package are employed, thena polymeric compatibilizer may be unnecessary. However, polymericcompatibilizers may be advantageously employed in the present invention.

[0077] 3. Substantially Random Interpolymers

[0078] Substantially random interpolymers comprise polymer units derivedfrom one or more α-olefin monomers with one or more vinyl or vinylidenearomatic monomers and/or a hindered aliphatic or cycloaliphatic vinyl orvinylidene monomers. The term substantially random as used herein meansthat the distribution of the monomers of said interpolymer can bedescribed by the Bernoulli statistical model or by a first or secondorder Markovian statistical model, as described by J. C. Randall inPOLYMER SEQUENCE DETERMINATION, Carbon-13 NMR Method, Academic Press NewYork, 1977, pp. 71-78. Preferably, substantially random interpolymers donot contain more than 15 percent of the total amount of vinyl orvinylidene aromatic monomer in blocks of vinyl or vinylidene aromaticmonomer of more than 3 units. More preferably, the interpolymer is notcharacterized by a high degree of either isotacticity orsyndiotacticity. This means that in the carbon⁻¹³ NMR spectrum of thesubstantially random interpolymer the peak areas corresponding to themain chain methylene and methine carbons representing either meso diadsequences or racemic diad (“r diad”) sequences should not exceed 75percent of the total peak area of the main chain methylene and methinecarbons.

[0079] Suitable α-olefins include for example, α-olefins described aboveas suitable for making α-olefin polymers. They preferably contain from 2to 12, more preferably from 2 to 8, carbon atoms. Particularly suitableare ethylene, propylene, butene-1, pentene-1, 4-methyl-1-pentene,hexene-1 or octene-1 or ethylene in combination with one or more ofpropylene, butene-1, 4-methyl-1-pentene, hexene-1 or octene-1. Theseα-olefins do not contain an aromatic moiety.

[0080] Suitable vinyl or vinylidene aromatic monomers that can beemployed to prepare the interpolymers include, for example, thoserepresented by the following formula:

[0081] wherein R¹ is selected from the group of radicals consisting ofhydrogen and alkyl radicals containing from 1 to 4 carbon atoms,preferably hydrogen or methyl; each R² is independently selected fromthe group of radicals consisting of hydrogen and alkyl radicalscontaining from 1 to 4 carbon atoms, preferably hydrogen or methyl; Aris a phenyl group or a phenyl group substituted with from 1 to 5substituents selected from the group consisting of halo, C₁₋₄-alkyl, andC₁₋₄-haloallkyl; and n has a value from zero to 4, preferably from zeroto 2, most preferably zero. Exemplary vinyl or vinylidene aromaticmonomers include styrene, vinyl toluene, α-methylstyrene, t-butylstyrene, chlorostyrene, including all isomers of these compounds, andthe like. Particularly suitable such monomers include styrene and loweralkyl- or halogen-substituted derivatives thereof. Preferred monomersinclude styrene, α-methyl styrene, the lower alkyl-(C₁-C₄) orphenyl-ring substituted derivatives of styrene, such as for example,ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes,para-vinyl toluene or mixtures thereof, and the like. A more preferredaromatic vinyl monomer is styrene.

[0082] By the term “hindered aliphatic or cycloaliphatic vinyl orvinylidene compounds”, it is meant addition polymerizable vinyl orvinylidene monomers corresponding to the formula:

[0083] wherein A¹ is a sterically bulky, aliphatic or cycloaliphaticsubstituent of up to 20 carbons, R¹ is selected from the group ofradicals consisting of hydrogen and alkyl radicals containing from 1 to4 carbon atoms, preferably hydrogen or methyl; each R² is independentlyselected from the group of radicals consisting of hydrogen and alkylradicals containing from 1 to 4 carbon atoms, preferably hydrogen ormethyl; or alternatively R¹ and A¹ together form a ring system. By theterm “sterically bulky” is meant that the monomer bearing thissubstituent is normally incapable of addition polymerization by standardZiegler-Natta polymerization catalysts at a rate comparable withethylene polymerizations. Preferred hindered aliphatic or cycloaliphaticvinyl or vinylidene compounds are monomers in which one of the carbonatoms bearing ethylenic unsaturation is tertiary or quaternarysubstituted. Examples of such substituents include cyclic aliphaticgroups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl oraryl substituted derivatives thereof, tert-butyl, norbornyl, and thelike. Most preferred hindered aliphatic or cycloaliphatic vinyl orvinylidene compounds are the various isomeric vinyl-ring substitutedderivatives of cyclohexene and substituted cyclohexenes, and5-ethylidene-2-norbomene. Especially suitable are 1-, 3-, and4-vinylcyclohexene.

[0084] Other optional polymerizable ethylenically unsaturated monomer(s)include norbornene and C₁₋₁₀ alkyl or C₆₋₁₀ aryl substitutednorbornenes. Exemplary substantially random interpolymers includeethylene/styrene, ethylene/styrene/propylene, ethylene/styrene/octene,ethylene/styrene/butene, and ethylene/styrene/norbomene interpolymers.

[0085] The substantially random interpolymers may be modified by typicalgrafting, hydrogenation, functionalizing, or other reactions well knownto those skilled in the art. The polymers may be readily sulfonated orchlorinated to provide functionalized derivatives according toestablished techniques.

[0086] The substantially random interpolymers may also be modified byvarious cross-linking processes including, but not limited to peroxide-,silane-, sulfur-, radiation-, or azide-based cure systems. A fulldescription of the various cross-linking technologies is described inU.S. Pat. No. 5,869,591 and U.S. Pat. No. 5,977,271, the entire contentsof both of which are herein incorporated by reference. Dual curesystems, which use a combination of heat, moisture cure, and radiationsteps, may be effectively employed. Such dual cure systems are disclosedand claimed in U.S. Pat. No. 5,911,940, which is incorporated herein byreference. For instance, it may be desirable to employ peroxidecrosslinking agents in conjunction with silane crosslinking agents,peroxide crosslinking agents in conjunction with radiation,sulfur-containing crosslinking agents in conjunction with silanecrosslinking agents, etc. The substantially random interpolymers mayalso be modified by various cross-linking processes including, but notlimited to the incorporation of a diene component as a termonomer in itspreparation and subsequent cross linking by the aforementioned methodsand further methods including vulcanization via the vinyl group usingsulfur for example as the cross linking agent.

[0087] The substantially random interpolymers include the pseudo-randominterpolymers as described in EP-A-0,416,815 by James C. Stevens et al.and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which areincorporated herein by reference in their entirety. The substantiallyrandom interpolymers also include the substantially random terpolymersas described in U.S. Pat. No. 5,872,201 which is incorporated herein byreference in their entirety. The substantially random interpolymers arebest prepared by polymerizing a mixture of polymerizable monomers in thepresence of one or more metallocene or constrained geometry catalysts incombination with various cocatalysts. Preferred operating conditions forthe polymerization reactions are pressures from atmospheric up to 3000atmospheres and temperatures from −30° C. to 200° C. Polymerizations andunreacted monomer removal at temperatures above the autopolymerizationtemperature of the respective monomers may result in formation of someamounts of homopolymer polymerization products resulting from freeradical polymerization.

[0088] Examples of suitable catalysts and methods for preparing thesubstantially random interpolymers are disclosed in EP-A-416,815;EP-A-514,828; EP-A-520,732; and EP-B-705,269; as well as U.S. Pat. No.:5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192;5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; and 5,470,993,all of which patents and applications are incorporated herein byreference.

[0089] The substantially random interpolymers usually contain from 0.5to 65, preferably from 1 to 55, more preferably from 1 to 50 molepercent of at least one vinyl or vinylidene aromatic monomer and/orhindered aliphatic or cycloaliphatic vinyl or vinylidene monomer andfrom 35 to 99.5, preferably from 45 to 99, more preferably from 50 to 99mole percent of ethylene and/or at least one aliphatic α-olefin havingfrom 3 to 20 carbon atoms.

[0090] The substantially random interpolymer(s) applicable to thepresent invention can have a melt index of from 0.01 to 1000, andpreferably from 0.01 to 100, more preferably from 0.05 to 50 grams per10 minutes (as determined by ASTM Test Method D1238, Condition190°/2.16).

[0091] While preparing the substantially random interpolymer, an amountof atactic vinyl or vinylidene aromatic homopolymer may be formed due tohomopolymerization of the vinyl or vinylidene aromatic monomer atelevated temperatures. The presence of vinyl or vinylidene aromatichomopolymer is in general not detrimental for the purposes of thepresent invention and can be tolerated. The vinyl or vinylidene aromatichomopolymer may be separated from the interpolymer, if desired, byextraction techniques such as selective precipitation from solution witha non-solvent for either the interpolymer or the vinyl or vinylidenearomatic homopolymer. For the purpose of the present invention it ispreferred that no more than 20 weight percent, preferably less than 15weight percent, most preferably less than 10 weight percent based on thetotal weight of the interpolymers of atactic vinyl or vinylidenearomatic homopolymer is present.

[0092] Most preferred as the second polymer component are thesubstantially random interpolymers such as those marketed by The DowChemical Company under the trademark INDEX™.

[0093] In a preferred embodiment, the foam of the present invention ismade from a blend of at least one substantially random interpolymer,such as an ethylene/styrene interpolymer, with an α-olefin polymer, suchas an ethylene polymer, such as LDPE. Suitable blends and processes formaking foams from the same are described in U.S. Pat. No. 6,160,029,which is incorporated herein by reference. The foams made from theseblends preferably have a density measured under DIN 53420 not greaterthan 40 kg/m³, preferably have an average cell size of at least 4 mm,preferably at least 5 mm, and preferably have a water absorption of lessthan 10 percent, more preferably less than 5 percent, by volume after 24hours immersion according to DIN 53433.

[0094] In another preferred embodiment, the foam of the presentinvention is made from a blend of at least one substantially randominterpolymer, such as an ethylene/styrene interpolymer, with an alkenylaromatic polymer, such as styrene. Suitable blends and processes formaking foams from the same are described in U.S. Pat. No. 6,187,232,which is incorporated herein by reference.

Prevaration of Foams

[0095] The foam structure of the invention may be prepared byconventional extrusion foaming processes. This process generally entailsfeeding the ingredients of the polymeric resin composition together orseparately into the heated barrel of an extruder, which is maintainedabove the crystalline melting temperature or glass transitiontemperature of the constituents of the blend; heating the polymericresin composition to form a plasticized or melt polymer material;incorporating a blowing agent into the melt polymer material to form afoamable gel; and expanding the foamable gel to form the foam product.The foamable gel may be extruded or conveyed through a die of desiredshape to an area of lower pressure where the mixture expands to form acellular foam structure. The lower pressure is preferably at anatmospheric level. Typically, the mixture is cooled to within +/−20° C.of the highest crystalline melting point or glass transition temperatureof the components of the polymer blend before extrusion in order tooptimize physical characteristics of the foam.

[0096] Processes for making ethylenic polymer foam structures aredescribed in C. P. Park. “Polyolefin Foam”, Chapter 9, Handbook ofPolymer Foams and Technology, edited by D. Klempner and K. C. Frisch,Hanser Publishers, Munich, Vienna, New York, Barcelona (1991), which isincorporated herein by reference.

[0097] A preferred process involves using a low die pressure forextrusion which is greater than the prefoaming critical die pressure butcan only go as high as four times, more preferably three times, evenmore preferably two times the prefoaming critical die pressure. Theprefoaming critical die pressure is best determined experimentally forformulations comprising not only the polymer components but alsoadditional additives such as flame retardants, synergists and cellenlarging agents. This is typically accomplished by preparing foams atseveral prefoaming die pressures and determining the effect of changesin the die pressure on the foam cell size and appearance. Below theprefoaming critical die pressure, the quality of the foam deterioratessharply, rough skin is observed on the foam due to rupture of surfacecells and typically a crackling noise is heard at the die due to rapiddegassing of the blowing agent. At too high die pressures, the foamtends to nucleate significantly causing a loss in cell size upper limitwhich typically corresponds to a value of up to four times, theprefoaming critical die pressure.

[0098] In another embodiment of the present invention, the resultingfoam structure is optionally formed in a coalesced strand form byextrusion of the ethylenic polymer material through a multi-orifice dieand wherein the die pressure for extrusion is greater than theprefoaming critical die pressure but can only go as high as four times,preferably three times, more preferably two times the prefoamingcritical die pressure. The orifices are arranged so that contact betweenadjacent streams of the molten extrudate occurs during the foamingprocess and the contacting surfaces adhere to one another withsufficient adhesion to result in a unitary foam structure. The streamsof molten extrudate exiting the die take the form of strands orprofiles, which desirably foam, coalesce, and adhere to one another toform a unitary structure. Desirably, the coalesced individual strands orprofiles should remain adhered in a unitary structure to prevent stranddelamination under stresses encountered in preparing, shaping, and usingthe foam. Apparatuses and method for producing foam structures incoalesced strand form are seen in U.S. Pat. Nos. 3,573,152and 4,824,720,both of which are incorporated herein by reference.

[0099] Alternatively, the resulting foam structure is convenientlyformed by an accumulating extrusion process as seen in U.S. Pat. No.4,323,528, which is incorporated by reference herein. In this process,low density foam structures having large lateral cross-sectional areasare prepared by: 1) forming under pressure a gel of the ethylenicpolymer material and a blowing agent at a temperature at which theviscosity of the gel is sufficient to retain the blowing agent when thegel is allowed to expand; 2) extruding the gel into a holding zonemaintained at a temperature and pressure which does not allow the gel tofoam, the holding zone having an outlet die defining an orifice openinginto a zone of lower pressure at which the gel foams, and an openablegate closing the die orifice; 3) periodically opening the gate; 4)substantially concurrently applying mechanical pressure by a movable ramon the gel to eject it from the holding zone through the die orificeinto the zone of lower pressure, at a rate greater than that at whichsubstantial foaming in the die orifice occurs and less than that atwhich substantial irregularities in cross-sectional area or shapeoccurs; and 5) permitting the ejected gel to expand unrestrained in atleast one dimension to produce the foam structure, and 6) wherein thedie pressure for extrusion is greater than the prefoaming critical diepressure where prefoaming occurs but can only go as high as four times,more preferably three times, even more preferably two times theprefoaming critical die pressure.

[0100] Blowing agents useful in making the resulting foam structureinclude inorganic agents, organic blowing agents and chemical blowingagents. Suitable inorganic blowing agents include carbon dioxide,nitrogen, argon, water, air, nitrogen, and helium. Organic blowingagents include aliphatic hydrocarbons having 1-9, preferably 1-6, carbonatoms, aliphatic alcohols having 1-3 carbon atoms, and fully andpartially halogenated aliphatic hydrocarbons having 14 carbon atoms.U.S. Pat. No. 6,048,909 to Chaudhary et al. discloses a number ofsuitable blowing agents at column 12, lines 6-56, the teachings of whichare incorporated herein by reference. Preferred blowing agents includealiphatic hydrocarbons having 1-9 carbon atoms, especially propane,n-butane and isobutane, more preferably isobutane.

[0101] The amount of blowing agent incorporated into the polymer meltmaterial to make a foam-forming polymer gel is typically from 0.2 to5.0, preferably from 0.5 to 3.0, and most preferably from 1.0 to 2.50gram moles per kilogram of polymer. However, these ranges should not betaken to limit the scope of the present invention.

[0102] The foam is conveniently extruded in various shapes having apreferred foam thickness in the direction of minimum foam thickness inthe range from about 1 mm to about 100 mm or more. When the foam is inthe form of a sheet, the foam preferably has a thickness in the rangefrom about 1 or 2 mm to about 15 mm. When the foam is in the form of aplank, the foam preferably has a thickness in the range from about 15 mmto about 100 mm. The desired thickness depends in part on theapplication.

[0103] When the foam of this invention is a thick sheet or plank, thefoam desirably has perforation channels. Perforation channels arepreferably not employed when the foam is a thin sheet. Thick polymerfoams may have an average thickness perpendicular to the surfaceperforated of at least about 25 millimeters (mm) and the polymer foammay be preferably perforated to an average depth of at least 5 mm belowthe surface of the polymer foam. Typically, perforation comprisespuncturing the base foam. A description of how to create suitableperforation channels to accelerate release of blowing agent from thefoam is provided in U.S. Pat. No. 5,585,058, which is incorporatedherein by reference. Accelerated aging of the foam to remove blowingagent may also be achieved, for example, by perforation techniques andheat aging as described in U.S. Pat. No. 5,242,016 to Kolosowski andU.S. Pat. No. 5,059,376 to Pontiff. Perforation of macrocellular foamsto improve acoustic performance of thermoplastic foams is described inWO 00/15697, which is also incorporated herein by reference.

[0104] The foam of this invention preferably has perforation channels,more preferably a multiplicity of perforation channels extending fromthe at least one surface into the foam such that there is an average ofat least one, preferably at least 5, more preferably at least 10, evenmore preferably at least 20, and even more preferably at least 30,perforation channel(s) per 10 square centimeters (cm²) area of the atleast one surface. The term “multiplicity” as used herein means at leasttwo. In a preferred embodiment, the foam of this invention contains atleast seven perforation channels.

[0105] The perforation channels preferably have an average diameter atthe at least one surface of at least 0.1 mm, more preferably at least0.5 mm, and even more preferably at least 1 mm and preferably up toabout the average cell size of the foam measured according to ASTMD3756. One or more surfaces of the foam preferably has an average of atleast four perforation channels per square centimeter extending from theat least one surface into the foam.

[0106] The polymer foam preferably has an average thicknessperpendicular to the surface perforated of at least 25 mm and thepolymer foam is preferably perforated to an average depth of at least 5mm below the surface of the polymer foam.

[0107] Typically, perforation comprises puncturing the base foam withone or more pointed, sharp objects. Suitable pointed, sharp objectsinclude needles, spikes, pins, or nails. In addition, perforation maycomprise drilling, laser cutting, high pressure fluid cutting, air guns,or projectiles.

[0108] In addition, the base foam may be prepared to have elongatedcells by pulling the foam during expansion. Such pulling results inelongated cells without changing or often, increasing the cell size inthe horizontal direction. Thus, pulling results in an increased averagecell size in the direction perpendicular to the vertical direction (EHaverage) and facilitates perforation.

[0109] Perforation of the base foam may be performed in any pattern,including square patterns and triangular patterns. Although the choiceof a particular diameter of the sharp, pointed object with which toperforate the base foam is dependent upon many factors, includingaverage cell size, intended spacing of perforations, pointed, sharpobjects useful in the preparation of certain foams of the presentinvention will typically have diameters of from 1 mm to 4 mm.

[0110] Compression may be used as an additional means of opening cells.Compression may be performed by any means sufficient to exert externalforce to one or more surfaces of the foam, and thus cause the cellswithin the foam to burst. Compression during or after perforation isespecially effective in rupturing the cell walls adjacent to thechannels created by perforation since a high pressure difference acrossthe cell walls can be created. In addition, unlike needle punching,compression can result in rupturing cell walls facing in all directions,thereby creating tortuous paths desired for sound absorption.

[0111] The mechanical opening of closed-cells of the base foam lowersthe airflow resistivity of the base foam by creating large-size pores inthe cell walls and struts. In any event, regardless of the particularmeans by which it does so, such mechanical opening of closed-cellswithin the base thermoplastic polymer foam serves to enhance theusefulness of the foam for sound absorption and sound insulationapplications.

[0112] Of course, the percentage of cells opened mechanically willdepend on a number of factors, including cell size, cell shape, meansfor opening, and the extent of the application of the means for openingapplied to the base foam.

[0113] The resulting foam structure preferably exhibits good dimensionalstability. Preferred foams recover 80 or more percent of initial volumewithin a month with initial volume being measured within 30 secondsafter foam expansion. Volume is measured by a suitable method such ascubic displacement of water.

[0114] In addition, a nucleating agent may optionally be added in orderto control the size of foam cells. Preferred nucleating agents includeinorganic substances such as calcium carbonate, talc, clay, titaniumoxide, silica, barium sulfate, diatomaceous earth, mixtures of citricacid and sodium bicarbonate, and the like. The amount of nucleatingagent employed may range from 0 to 5 phr.

[0115] In one embodiment, the foam structure may be substantiallycross-linked. Cross-linking may be induced by addition of across-linking agent or by radiation. Induction of cross-linking andexposure to an elevated temperature to effect foaming or expansion mayoccur simultaneously or sequentially. If a cross-linking agent is used,it is incorporated into the polymer material in the same manner as thechemical blowing agent. Further, if a cross-linking agent is used, thefoamable melt polymer material is heated or exposed to a temperature ofpreferably less than 150° C. to prevent decomposition of thecross-linking agent or the blowing agent and to prevent prematurecross-linking. If radiation cross-linking is used, the foamable meltpolymer material is heated or exposed to a temperature of preferablyless than 160° C. to prevent decomposition of the blowing agent. Thefoamable melt polymer material is extruded or conveyed through a die ofdesired shape to form a foamable structure. The foamable structure isthen cross-linked and expanded at an elevated or high temperature(typically, 150° C.-250° C.) such as in an oven to form a foamstructure. If radiation cross-linking is used, the foamable structure isirradiated to cross-link the polymer material, which is then expanded atthe elevated temperature as described above. The present structure canadvantageously be made in sheet or thin plank form according to theabove process using either cross-linking agents or radiation.

[0116] Crosslinked acoustically active thermoplastic macrocellular foamsand methods for manufacturing them are described in more detail in WO00/15700, which is incorporated herein by reference.

[0117] The present foam structure may also be made into a continuousplank structure by an extrusion process utilizing a long-land die asdescribed in GB 2,145,961A. In that process, the polymer, decomposableblowing agent and cross-linking agent are mixed in an extruder, heatingthe mixture to let the polymer cross-link and the blowing agent todecompose in a long-land die; and shaping and conducting away from thefoam structure through the die with the foam structure and the diecontact lubricated by a proper lubrication material

[0118] In a preferred embodiment of the present invention, themacrocellular thermoplastic polymer foams have less than 35 percentcrosslinking after 10 days aging. The resulting foam structure morepreferably has not more than 30 percent crosslinking, even morepreferably less than 20 percent crosslinking, and even more preferablyless than 10 percent crosslinking, after 10 days aging. The foam of thisinvention is even more preferably substantially noncrosslinked oruncrosslinked and the polymer material comprising the foam structure ispreferably substantially free of crosslinking.

[0119] The resulting foam structure may be either closed-celled oropen-celled. The open cell content will range from 0 to 100 volumepercent as measured according to ASTM D2856-A.

[0120] The resulting foam structure preferably has a density of lessthan 300, preferably less than 100, more preferably less than 60 andmost preferably from 10 to 50 kilograms per cubic meter.

[0121] The macrocellular foams exhibit an average cell size of at least1.5 mm, preferably 2 mm, more preferably at least 3 mm, even morepreferably at least 4 mm, preferably up to 20 mm, 15 mm and 10 mm alsobeing preferred, according to ASTM D3575.

Properties and End Uses

[0122] Applications for the macrocellular flame resistant acousticcompositions of the present invention include articles made by all thevarious extrusion processes. Such articles may be used in automotive andother transportation devices, building and construction, household andgarden appliances, power tool and appliance and electrical supplyhousing, connectors, and aircraft as acoustic systems for soundabsorption and insulation. The materials are especially suited toapplications where, in addition to meeting the relevant acousticperformance standards, they must also meet any applicable fire testcodes, for example office partitions, automotive decouplers, domesticappliance sound insulation, and sound proofing panels and machineenclosures. The ability to pass the US FMVSS 302 (auto) test, have a USUnderwriter's Laboratory UL 94 rating of IF1, and a B1 rating underGerman norm DIN 4102 are some of the goals that may be achieved with thepresent invention.

[0123] The foams of the present invention have excellent acousticabsorption capabilities. One way to measure the ability to absorb soundis to measure the acoustic absorption coefficient of the foam accordingto ASTM E1050 at sound frequencies of 250, 500, 1000 and 2000 Hz andthen calculate the arithmetic average of those sound absorptioncoefficients. When that determination is made with the foams of thepresent invention, the average sound absorption coefficient is greaterthan 0.15, preferably greater than 0.20, more preferably greater than0.25, even more preferably greater than 0.30. Thus the foams of thisinvention are useful for absorbing sound in the range from 250 to 2000Hz such that the sound absorption capability is equivalent to theforegoing preferred average sound absorption coefficients. For example,the foam may be located in the presence of a sound intensity of at least50 decibels, such as on a vehicle equipped with a combustion engine.Unexpectedly, foams of the present invention have a peak absorptioncoefficient of at least 0.5 within a frequency range of 250 to 1000 Hz,for foams having a thickness within a range of from 10 mm to 100 mm.

[0124] Another advantage of the foam of the present invention is thatthe high average sound absorption coefficient may be achieved with a lowwater absorption. That is desirable to help limit corrosion of proximatemetal parts, to avoid the growth of bacteria and mold, and to improvethermal insulation value where that is needed. The inventive foampreferably does not absorb more than 10 percent water by volume, 5percent water by volume, 3 percent water by volume, more preferably notmore than 1.5 percent water by volume, and even more preferably not morethan 1 percent water by volume, when measured according to European Norm(EN) 12088 at a 50° C. temperature gradient between a warm,water-saturated atmosphere and the foam (the latter of which ismaintained at a temperature at or below about 0° C. in order to condensethe water onto the surface of the foam sample) based on a test period of14 days exposure.

[0125] The foregoing list merely illustrates a number of suitableapplications. Skilled artisans can readily envision additionalapplications without departing from the scope or spirit of the presentinvention.

[0126] The following examples illustrate, but do not in any way limitthe scope of the present invention.

EXAMPLES Materials Used to Prepare the Foams of the Examples

[0127] 1. LDPE 1 is a low density polyethylene (LDPE) resin with adensity of 0.924 g/cm3 and melt index of 0.88 dg/min (according to ASTMD1238, 190° C./2.16 kg).

[0128] 2. LDPE 2 is which is a low density polyethylene (LDPE) with adensity of 0.924 g/cc and melt index of 0.8 dg/min (according to ASTMD1238, 190° C./2.16 kg) and is commercially available as LDPE 300R fromthe Dow Chemical Company.

[0129] 3. LDPE 3 is commercially available as LDPE 400R which is a lowdensity polyethylene (LDPE) with a density of 0.925 g/cc and melt indexof 1.0 dg/min (according to ASTM D1238, 190° C./2.16 kg) and availablefrom the Dow Chemical Company.

[0130] 4. LDPE 4 is commercially available as LDPE 620i which is a lowdensity polyethylene (LDPE) with a density of 0.924 g/cc and melt indexof 1.8 dg/min (according to ASTM D1238, 190° C./2.16 kg) and availablefrom the Dow Chemical Company.

[0131] 5. HMS PP 1 is commercially available as Profax PF814 which is ahigh melt strength polypropylene with a melt index of 3 dg/min(according to ASTM D1238, 230° C./2.16 kg) and available from MontellPolyolefins.

[0132] 6. PE-68™ is a brominated fire retardant having 68 wt percentbromine content (tetrabromobisphenol A bis (2,3-dibromopropyl ether)(used as a 30 percent concentrate in LDPE) and is a trademark of andavailable from the Great Lakes Chemical Corporation.

[0133] 7. CHLOREZ™ 700 is a chlorinated paraffin containing 71.5 wtpercent chlorine and is a trademark of and available from the DoverChemical Corporation.

[0134] 8. TRUTINT™ 50 is antimony trioxide synergist, Sb2O3, of averageparticle size of 3.0 microns, respectively (used as an 80 percentconcentrate in LDPE) and is a trademark of and available from the GreatLakes Chemical Corporation.

[0135] 9. TMS™ is antimony trioxide (Sb2O₃) synergist having an averageparticle size of 1.5 microns (used as an 80 percent concentrate in LDPE)and is a trademark of and available from the Great Lakes ChemicalCorporation.

[0136] 10. MICROFINE™ AO-3 is antimony trioxide (Sb2O ₃) synergisthaving an average particle size of 0.3 microns (used as an 80 percentconcentrate in LDPE) and is a trademark of and available from the GreatLakes Chemical Corporation.

[0137] 11. NYACOL™ DP-6215 is antimony pentoxide synergist of averageparticle size 0.03 microns (used as a concentrate in high melt flow PP)and is a trademark of and available from Nyacol Nano Technologies, Inc.

[0138] 12. IRGANOX™ 1010 is a phenolic antioxidant/stabilizer and is atrademark of and available from Ciba Specialty Chemicals

[0139] 13. ULTTRANOX™ 815A is a phenolic/phosphiteantioxidant/stabilizer and is a trademark of and available from GESpecialty Chemicals

[0140] 14. ATMER™ 129 and 1013 are glycerol mono stearate, apermeability modifier/cell size enlarger, and is a trademark of andavailable from ICI Americas

[0141] 15. PLASBLAK™ PE3037 is a 25 percent carbon black concentrate(pigment) in LDPE resin and is a trademark of and available from CabotPlastics International

[0142] 16. 50 BK 70 is a 25 percent carbon black concentrate (pigment)compounded in LDPE resin and custom made by M.A. Hanna Inc.

[0143] Tests for the examples below were conducted by extruding theformulations specified in the respective Tables 1 to 5 on an extrusionline. The extrusion line consists of a single screw extruder with afeeding zone for resins and solid additives, a melting zone, and ametering zone. In addition, there is a mixing zone with a port forinjecting blowing agents and liquid additives and a cooling zone touniformly cool the melt to the foaming temperature. The foamingtemperature is the optimal gel temperature for foaming when the meltstrength is high enough to stabilize the foam and prevent cell collapse.The line also consists of a gear pump between the metering and mixingzones to stabilize the melt flow and a static mixer in the cooling zoneto aid in gel temperature uniformity. The melt is extruded through a dieto ambient temperature and pressure to expand the gel to the desiredshape and stabilize the foam.

Example 1

[0144] The following example illustrates the effect of particle size ofan additive (antimony trioxide, synergist) on the cell size of theresulting foam. The example also details fire retardant formulations toprepare PP/PE blend acoustical foams of the invention and methods ofpreparing such foams by the extrusion process. The foams listed in Table1 were prepared in standard extrusion equipment. The levels of theadditives used in the formulation (irrespective of whether they are fedas powders or as concentrates) are reported in phr. The level of blowingagent used in the formulation is reported in parts by weight per hundredparts by weight of the total feed (polymer and additives) (pph).

[0145] The comparative formulation 1 in Table 1 was run with a 60percent/40 percent blend (by weight) of HMS PP 1 and LDPE 1; with thefollowing additives: 0.5 phr Irganox 1010, 0.2 phr Ultranox 815A, 0.5phr Atmer 129 GMS, 0.4 phr 50 BK 70 carbon black, 5 phr PE-68 brominatedfire retardant and 0.5 phr antimony trioxide synergist. The level ofisobutane blowing agent was 6.5 pph. The antimony trioxide concentratewas prepared by mixing 7.5 percent by weight (wt %), based onconcentrate weight GMS and 30 wt % 3.0μ TRUTIT-50 grade of Sb2O3 in aHenschel mixer and compounding with 62.5 wt % LDPE 4 in a twin screwextruder. The temperature and pressure profile used for the PP/PE blendfoam was similar to that used for standard PP foam, except for the diepressure that was maintained as low as possible, close to the prefoaminglimit. The highest gel temperature in the line was at the mixer (225°C.) and the highest gel pressure was at the gear pump (1780 psi). Thefoaming temperature was 152° C.

[0146] Using the same line conditions, the same formulation was run witha new Sb2O3 concentrate at the same loading (PE-68 to Sb2O3 ratio of 5phr:0.5 phr) as Example la of the present invention and at twice theloading (PE-68 to Sb2O3 ratio of 5 phr:1 phr) as Example 1b of thepresent invention. This concentrate was prepared by compounding 80 wt %0.31 MICROFINE AO-3 grade of Sb2O3 (treated by physical processing) with20 wt % LDPE 4 in a twin screw extruder. The results are summarized inTable 1 below. TABLE 1 Flame Ave. Base resins Fire retardant cellExample* and wt. Ratio retardant synergist size Control 1 HMS PP 1:LDPE1 = 60:40 PE-68 0 phr n/a 0 phr 7.5 mm Comp. 1 HMS PP 1:LDPE 1 = 60:40PE-68 5 phr TRUTINT 50 0.5 phr 1.5 mm 1a HMS PP 1:LDPE 1 = 60:40 PE-68 5phr MICROFINE AO-3 0.5 phr 10.2 mm 1b HMS PP 1:LDPE 1 = 60:40 PE-68 5phr MICROFINE AO-3 1 phr 8.8 mm

[0147] The Control 1 formulation with no FR package was run initiallyand the cells were large (average cell size: 7.5 mm). After theComparative Example 1 fire retardant had purged through the line, theaverage cell size decreased significantly to 1.5 mm because ofnucleation induced by the 3 micron Sb2O3 particles.

[0148] The average cell size dramatically increased to 10.2 mm after theExample 1a MICROFINE 0.3 micron particle size concentrate had purgedthrough the line. The average cell size stabilized at 8.8 mm after theExample 1b MICROFMIE 0.3 micron particle size concentrate at higherloading had purged through the line. Thus, the use of the sub-microngrade of Sb2O3 in the formulation increased the average cell size of thefoam and permitted higher loading of the fire retardant synergist forimproved fire retardancy.

Example 2

[0149] The following example illustrates the effect of particle size ofan additive (antimony trioxide, synergist) on the cell size of theresulting foam. The example also details fire retardant formulations toprepare PE acoustical foams of the invention and methods of preparingsuch foams by the extrusion process. The foams listed in Table 2 wereprepared in standard extrusion equipment.

[0150] Comparative Example 2 contains 100 wt % LDPE 2 with the followingadditives: 0.3 phr lrganox 1010; 1.0 phr Atmer 1013 GMS; 11 phr of PE-68brominated FR; 1.3 phr of 3μ Trutint 50 Sb2O3 and 0.375 phr of 25 wt %Plasblak PE3037carbon black. The level of isobutane blowing agent was8.3 pph. The temperature and pressure profile used was the same as thatused for standard polyethylene foam, except for the die pressure thatwas maintained as low as possible, close to the prefoaming limit. Thehighest gel temperature in the line was at the extruder (192° C.) andthe highest gel pressure was at the gear pump (122 bar). The foamingtemperature was 1111° C.

[0151] Using similar line conditions, a comparable formulation with 0.8phr Atner 1013 GMS and 9.0 pph isobutane was run with a new Sb2O3 at ahigher loading of 2 phr as Example 2A of the present invention. Thisconcentrate was prepared by compounding 80 wt % 0.3μ MICROFINE AO-3grade of Sb2O3 (treated by physical processing) with 20 wt % LDPE 4(based on concentrate weight) in a twin screw extruder. In this case,the highest gel temperature in the line was at the extruder (185° C.)and the highest gel pressure was at the gear pump (117 bar). The foamingtemperature was 112° C.

[0152] Again using the same line conditions, the Example 2B formulationwas ran with a higher loading of 3 phr Sb2O3.

[0153] The results obtained with the above examples are summarized inTable 2 below. TABLE 2 Flame Ave. Base Fire retardant cell Example*resin retardant synergist size Control 2a* LDPE 2 PE-68 0 phr n/a 0phr >10 mm Comp. 2* LDPE 2 PE-68 11 phr TRUTINT 50 1.3 phr 7.7 mmControl 2b** LDPE 2 PE-68 0 phr n/a 0 phr >10 mm Ex 2A** LDPE 2 PE-68 11phr MICROFINE AO-3 2 phr 9.1 mm Ex 2B** LDPE 2 PE-68 6 phr MICROFINEAO-3 3 phr 7.7 mm

[0154] The Control 2a formulation with no FR package was run initiallyand the cells were large (average cell size: >10 mm). After theComparative Example 2 fire retardant was purged in, the cells becamesmaller because of nucleation induced by the 3 micron Sb2O3 particles.The Sb2O3 level had to be limited to 1.3 phr to achieve foam with cellsize of>6 mm. At higher levels of Sb2O3, the foam had unacceptably smallcell size and marginal acoustical activity.

[0155] The Control 2b formulation with no FR package was run initiallyand the cells were large (average cell size: >10 mm). The average cellsize of the foam stabilized at 9.1 mm after the 0.3 micron MICROFINEAO-3 concentrate of Example 2A had purged through the line.

[0156] When the 0.3 micron MICROFINE AO-3 concentrate of Example 2B hadpurged through the line, the average cell size of the foam stabilized at7.7 mm Thus, the use of the sub-micron grade of Sb2O3 in the formulationsignificantly reduced the nucleation potential of the synergist andpermitted higher loading for improved fire retardancy.

Example 3

[0157] The following example illustrates the effect of particle size ofan additive (antimony oxide, synergist) on the cell size of theresulting foam. The foams listed in Table 3 were prepared in standardextrusion equipment.

[0158] A 60%/40% blend (by weight) of HMS PP 1 and LDPE 4, 0.3 phrIrganox 1010; 0.5 phr Atmer 129 GMS; 5 phr PE-68 brominated FR; 1 phrTRUTINT 50 grade Sb2O3 (3.0μ) and 8 pph isobutane were combined in anextruder to make Comparative Example 3. The temperature and pressureprofile used was the same as that used for standard polypropylene foam,except for the die pressure that was maintained as low as possible,close to the prefoaming limit.

[0159] The 3.0μ Sb2O3 was replaced at the same antimony loading with thesub-micron MICROFINE AO-3 grade (0.3μ) to make Example 3A of the presentinvention.

[0160] The 0.3μ Sb2O3 was replaced at the same antimony loading with thenano-sized NYACOL grade Sb2O5 (0.03μ) to make Example 3B.

[0161] The formulations and results are summarized in Table 3 below.TABLE 3 Flame Ave. Fire retardant cell Example* Base resins and ratioretardant synergist size Comp. 3* HMS PP 1:LDPE 4=60:40 PE-68 5 phrTRUTINT 50 1 phr 4.5 mm Ex 3A* HMS PP 1:LDPE 4=60:40 PE-68 5 phrMICROFINE AO-3 1 phr 5.4 mm Ex 3B* HMS PP 1:LDPE 4=60:40 PE-68 5 phrNYACOL DP-6215 1 phr 6.2 mm

[0162] The foam of Example 3A had an average cell size of 5.4 mm, whichrepresents an improvement in average cell size over Comparative Example3.

[0163] The foam of Example 3B with even smaller particle size had anaverage cell size of 6.2 mm, which is comparable to the Control 3formulation with no synergist.

[0164] The results show that as the particle size of the inorganicadditive is decreased below one micron, the nucleation propensitysurprisingly reduces, resulting in foam with larger cell size.

Example 4

[0165]100 wt % LDPE 3; 0.1 phr Irganox 1010; 0.2 phr Atmer 129 GMS; 0.3phr Plasblak PE3037 carbon black; 4.1 phr PE-68 brorninated FR; 2 phrTMS grade Sb2O3 (1.5μ); 2 phr Chlorez 700 chlorinated FR and 9 pphisobutane were combined to make Comparative Example 4A. The temperatureand pressure profile used was the same as that used for standardpolyethylene foam, except for the die pressure that was maintained aslow as possible, close to the prefoaming limit. The resulting foam hadan average cell size of 6.3 mm.

[0166] The Sb2O3 was replaced by the larger particle size TRUTINT 50grade (3.0μ) at a higher level, 2.3 phr, without the chlorowax to makeComparative Example 4B. The resulting foam had an average cell size of7.1 mm.

[0167] The results are summarized in Table 4 below. TABLE 4 Flame Ave.Base Fire retardant cell Example* resin retardant synergist size Comp.4A LDPE 3 PE-68 4.1 phr TMS (1.5μ) 2 phr 6.3 mm Chlorez-700 2 phr Comp.4B LDPE 3 PE-68 4.1 phr Trutint-50 (3.0μ) 2.3 phr 7.1 mm

[0168] As can be seen from the above data, an increase in flameretardant synergist average particle size resulted in an increase inaverage cell size. This data confirms the expected result, namely that adecrease in particle size is expected to decrease the average cell sizefor a given weight percent concentration of the synergist. That is incontrast to the unexpected increase in average cell size shown in Table2, for example.

Example 5

[0169] A 60 percent/40 percent blend (by weight) of HMS PP 1 and LDPE 3;0.1 phr Irganox 1010; 0.3 phr Plasblak PE3037 carbon black; 3 phr PE-68brominated FR; 1 phr TMS grade Sb2O3 (1.5μ); 1 phr Chlorez 700chlorinated FR and 10 pph isobutane were combined to make ComparativeExample 5A. The temperature and pressure profile used was the same asthat used for standard polypropylene foam, except for the die pressurethat was maintained as low as possible, close to the prefoaming limit.The resulting foam had an average cell size of 3.6 mm.

[0170] The Sb2O3 was replaced by the larger particle size TRUTINT 50grade (3.0μ) at the same level, 1 phr, without the chlorowax to makeComparative Example 5B. The resulting foam had an average cell size of6.5 mm.

[0171] The results are summarized in Table 5 below. TABLE 5 Flame Ave.Fire retardant cell Example* Base resins and ratio retardant synergistsize Comp. 5A HMS PP 1:LDPE 3=60:40 PE-68 3 phr TMS (1.5μ) 1.0 phr 3.6mm CHLOREZ- 1 phr 700 Comp. 5B HMS PP 1:LDPE 3=60:40 PE-68 3 phrTRUTINT-50 1.0 phr 6.5 mm (3.0μ)

[0172] As can be seen from the above data, an increase in flameretardant synergist average particle size resulted in an increase inaverage cell size. This data confirms again the expected result, namelythat a decrease in particle size is expected to decrease the averagecell size for a given weight percent concentration of the synergist.That is in contrast to the unexpected increase in average cell sizeshown in Table 3, for example.

Example 6

[0173]100 wt % LDPE 3; 0.3 phr Atmer 1013 GMS; 1 phr TMS grade Sb2O3(l.5μ) and 10 pph isobutane were combined to make Comparative Example6A. The temperature and pressure profile used was the same as that usedfor standard polyethylene foam, except for the die pressure that wasmaintained as low as possible, close to the prefoaming limit. Theresulting foam had an average cell size of 2.7 mm.

[0174] The Sb2O3 was replaced by the larger particle size TRUTINT 50grade (3.0μ) at the same level, 1 phr, to make Comparative Example 6B.The resulting foam had an average cell size of 3.2 mm.

[0175] The results are summarized in Table 6 below. TABLE 6 Flame Ave.Base Fire retardant cell Example* resin retardant synergist size Comp.6A LDPE 3 PE-68 0 phr TMS (1.5μ) 1 phr 2.7 mm Comp. 6B LDPE 3 PE-68 0phr Trutint-50 (3.0μ) 1 phr 3.2 mm

[0176] As can be seen from the above data, an increase in flameretardant synergist average particle size resulted in an increase inaverage cell size. This data confirms the expected result, namely that adecrease in particle size is expected to decrease the average cell sizefor a given weight percent concentration of the synergist. That is incontrast to the unexpected increase in average cell size shown in Table1, for example.

1. A cellular polymer foam having an average cell size according to ASTMD3575 of at least 1.5 mm, the foam containing at least one flameretardant adjuvant, wherein the flame retardant adjuvant has an averageparticle size less than one micron.
 2. The polymer foam of claim 1,wherein the particle size of the flame retardant adjuvant is less than0.5 micron.
 3. The polymer foam of claim 1 or 2, wherein the flameretardant adjuvant comprises an oxide of antimony.
 4. The polymer foamof any one of the preceding claims further comprising a flame retardant.5. The polymer foam of claim 4, wherein the flame retardant is ahalogen-containing organic compound.
 6. The polymer foam of any one ofthe preceding claims having not more than 30 percent crosslinking after10 days aging.
 7. The polymer foam of any one of the preceding claims,wherein the polymer comprises at least 50 percent polypropylene.
 8. Thepolymer foam of any one of the preceding claims, wherein the polymerfoam has at least one surface, the at least one surface having definedtherein a multiplicity of perforation channels extending from the atleast one surface into the foam such that there is an average of atleast one perforation channel per 10 square centimeters of the at leastone surface.
 9. The polymer foam of any of the preceding claims, whereinthe polymer is a thermoplastic polymer.
 10. A process for makingcellular polymer foams comprising extruding at an elevated temperature afoamable gel from a first region having a first pressure into a secondregion having a second pressure less than the first pressure to allowexpansion of the foamable gel, the foamable gel comprising at least onethermoplastic polymeric resin, at least one blowing agent, at least oneflame retardant and at least one flame retardant adjuvant, wherein thesolid particulate flame retardant adjuvant has a particle size less than1 micron.
 11. The process of claim 10, wherein the polymer is athermoplastic polymer.
 12. A method for increasing the maximum amount ofsolid particulate flame retardant adjuvant in cellular foams having agiven average cell size according to ASTM D3575 of at least 1.5 mmcomprising decreasing the average particle size of the solid particulateflame retardant adjuvant to smaller average particle size that is lessthan 1 micron.
 13. The method of claim 12, wherein the cellular foam isa thermoplastic cellular foam.